获取WPF扩展器头的高度

Expander { Border { DockPanel { ToggleButton, ContentPresenter {...} } } }

VisualTreeHelper

var border = VisualTreeHelper.GetChild(expander, 0);
var dockpanel = VisualTreeHelper.GetChild(border, 0);
var togglebutton = VisualTreeHelper.GetChild(dockpanel, /*0*/); // it may be not 0th, so please enumerate all children using VisualTreeHelper.GetChildrenCount(dockpanel) and find that ToggleButton
return togglebutton.ActualHeight;

ActualHeight

Height

Height

double.IsNaN

auto